Add a python script to install Direct3D 12 SDK components.

This makes it much faster to get started with Direct3D 12 builds,
as you only need to run `python .\misc\scripts\install_d3d12_sdk_windows.py`
then run `scons d3d12=yes`.

This installs DirectX Shader Compiler, Mesa NIR, WinPixEventRuntime
and DirectX 12 Agility SDK.

- Define a default path that uses the locations from the script.
- Now the default path is in "%LOCALAPPDATA%\Godot\build_deps\"
- Updated CI to use this new python script.

Co-Authored-By: Hugo Locurcio <hugo.locurcio@hugo.pro>

.github/workflows/windows_builds.yml

@@ -7,7 +7,7 @@ on:
 env:
   # Used for the cache key. Add version suffix to force clean build.
   GODOT_BASE_BRANCH: master
-  SCONSFLAGS: verbose=yes warnings=extra werror=yes module_text_server_fb_enabled=yes d3d12=yes "dxc_path=${{github.workspace}}/dxc" "mesa_libs=${{github.workspace}}/godot-nir-static"
+  SCONSFLAGS: verbose=yes warnings=extra werror=yes module_text_server_fb_enabled=yes d3d12=yes
   SCONS_CACHE_MSVC_CONFIG: true
 
 concurrency:
@@ -49,27 +49,8 @@ jobs:
       - name: Setup python and scons
         uses: ./.github/actions/godot-deps
 
-      - name: Download pre-built DirectX Shader Compiler
-        uses: dsaltares/fetch-gh-release-asset@1.0.0
-        with:
-          repo: Microsoft/DirectXShaderCompiler
-          version: tags/v1.7.2308
-          file: dxc_2023_08_14.zip
-          target: dxc.zip
-
-      - name: Extract pre-built DirectX Shader Compiler
-        run: 7z x dxc.zip -o${{github.workspace}}/dxc
-
-      - name: Download pre-built Mesa-NIR
-        uses: dsaltares/fetch-gh-release-asset@1.0.0
-        with:
-          repo: godotengine/godot-nir-static
-          version: tags/23.1.0-devel
-          file: godot-nir-23.1.0-1-devel.zip
-          target: godot-nir-static.zip
-
-      - name: Extract pre-built Mesa-NIR
-        run: 7z x godot-nir-static.zip -o${{github.workspace}}/godot-nir-static
+      - name: Download Direct3D 12 SDK components
+        run: python ./misc/scripts/install_d3d12_sdk_windows.py
 
       - name: Setup MSVC problem matcher
         uses: ammaraskar/msvc-problem-matcher@master